Electric circuit control means



Nov. 19, 1935. c. G: SUITS ELECTRIC CIRCUIT CONTROL MEANS Original Filed nay 26, 1932 Fig.5,

FREQ-VOLTAGE l I V VOLTAGE 0 VOL'X'AGE VARYTNG' WITH FREQ.

X VOLTAGE CONSTANT -u W W b 4 m mm .8. a m D a w F Patented Nov. 19, 1935;

UNITED STATES P ATs roFHcs' 2.021.154 v *mcrmc cmcUrr comm. mums Chauncey G. Suits, SchenectadyyN. Y., asaignor to General Electric mm, a corporation of New York lO. tion and control of electricacircuits and rotating machines which require a frequency responsive means which functions in response to either voltage or frequency provided the ratio between these quantities is proportional. There are also certain other electric applicationswhich require fre:

quency responsive means but the electric type of this class of apparatus is usually aifectedby v'ariations in the voltage applied thereto so that the frequency response is not independent of voltage.-

In accordance with my invention I employ cir-' cuit elements having a non-linear volt-ampere characteristic arranged in various combinations with capacitance andresistance elements in an electric network energized from an alternating current source in such a manner that an output voltage is obtained which varies critically in accordance with variations in the frequency of the source of supply. Electric circuits comprising circuit elements of inductance, capacitance and resistance which depend upon current are distinguished by non-linear volt-ampere characteristics. Throughout the specification and claims non-linear element or circuit will be used to indicate an element, circuit, or branch circuit having a non-linear volt-ampere characteristic for effective values of alternating current. Certain.

unusual resonance effects occur in circuits of this type employing an iron core inductance with a substantiallyclosed core. These effects are strikingly different from the well known properties of resonance circuits where the flux path of the inductance element is almost wholly in air. In the well known series resonant linear circuit of I inductance, capacitance and resistance the volt-,

age across the inductance is equal and opposite to.

the voltage across the capacitance throughout the voltage cycle. Similarly, for the parallel resonant linear circuit the inductive current and capacitive current are equal throughoutthe current cycle. For the non-linear circuit, with an inductance variable with current in combination with a capacitance, the condition of resonance is satisfied for only a limited portion of the volta e or r nt ycle. Resonance a non-linear 1 application m, 20, 1932, Serial No. Divided and this application-April 28, ms, Serial No. 608,011

8 (Cl. iii-no) circuits is thus regarded aspartial and because of thischaracteristic the terminology "non-linear resonance" is employed in the claims-to distinguish the subject matter of the claims from-linear circuits of the same general type. 5

It is an object of my invention to provide an t ,improved' frequency regulating system for electric circuits and rotating machines.

My invention will be better understood from the following descriptionv tal ren in connection 10 with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. l is a' diagrammatic illustration of an elementary series-type non-linear circuit arrangement empioyedincarrying out my 15 invention; Figs. 2 and 3 are illustrative curves to aidin understanding operating characteristics of various embodiments of my invention; Fig. 4. is an embodiment ofmyinventionas applied in regulating the speed of a prime mover; Fig.5 is 20 a modification of the embodiment illustrated in ,Fig. 4; Fig. 6 is an embodiment oi my invention as applied in regulating a directcurren't dynamo electric machine; Fig. 7 is a diagrammatic illustration of an elementary parallel-type non-linear 5 circuit arrangement which may be employed in carrying out my invention; Fig. 8 is an illustrative curve for-explaining the operating characteristics of the elementary circuit arrangement shown in Fig. 7; Fig. 9 is a parallel and a series-type non-linear circuit in combination which may be employed in lieu of the simple series circuit shown in Figs. 4, 5 and 6; Fig. 10 is another arrangement utilizing a series-parallel type of non-linear circuit which may be employed as the frequency 35 sensitive control element of the embodiments of my invention illustrated in Figs. 4, 5 and 6; Fig. 11 is an illustrative curve for explaining an operating characteristic of the circuit arrangement of Fig. 10, and Fig. 12 is a modification of the ar- 40 rangement illustrated in Fig. 10.

Referring to Fig. 1 of the drawing, Ill indicates a variable frequency source of alternating voltage which is connected to energize an electric network comprising a saturable inductance II, a 45 capacitance l2, and a resistance It, connected in series relation across the source Ill. An electroresponsive device or relay mechanism comprising a winding i4 and a cooperating member or armature I5 is connected to be energized in accordance with the voltage across the resistance l3 but it will be evident from the discussion following thatit may equally well be connected across the capacitance 12 or in series with the capacitance, inductance and resistance. It may after pointed out.

thisis not as desirable for the reasons herein- When the voltage of the source ll varies in proportion to the frequencythe curves of Fig. 2 are obtained for the circuit of Fig. 1. In Fig. 2. the sries current and voltages across the different elements of the circuit are plotted as timetions of the variable applied voltage which is proportional to frequency. It will be observed that a variation of these quantities with frequency bears a roughanalogy to the change in the same quantities for a linear circuit with the exception that there is a region wherein a critical change takes place from a resonant condition to a dissonant condition or vice versa In general, the change in current-I, the change in inductance voltage Er, or the change in capacitance voltage Ec, is sufficiently great to allow a relay, contactor or other electro-responsive mechanism to be turned on and of! ,at a critical frequency. A

Consider the arrangement illustrated in Fig 1 in which the winding ll of the relay mechanism is energized in parallel with the resistance l2. The-voltage applied to the relay-from the resistance will vary in the manner indicated by the curve I of Fig. 2 which has been replotted in Fig. 3. For the armature and solenoid alone the voltage required to pick up or "release the armature is approximately proportional to frequency. It may be seen, therefore, that if'the frequency increases from a small value, the solenoid is energized and the armature is picked up v at the frequency h, and remainsin this condition until the frequency exceeds {1. For-decreasing frequency, the armature is again picked up at the frequency f1, and released at the frequency ,f3,- which differs from the frequency 1:, by a small amount. When the relay is energized inparallel with the capacitance of. the same series circuit, it may be seen from similar considerations that the solenoid will be energized for all frequencies less than the critical frequency for the circuit. The third pouibility, that of using the voltage across the inductance II. to actuate the relay, is not very suitable since the change in inductive voltage in the critical regionis relatively small due to the saturation property of this element.

. In a particular circuit of the type shown in Fig. l observations were taken in which the critical region occurred at a frequency of approximately 61 cycles which may be taken to represent the frequency f1 of Fig. '3. For frequencies between 50 and 61 cycles the current in the circuit was a maximum indicated by the region mm. For frequencies less than 50 the current decreased'in a somewhat linear manner to zero. In addition to the rapid change in magnitude of the current at the critical frequency there is 'avcorresponding rapid change in phase of the current in the same region. Thus for frequencies higher than 61 cycles, with the circuit constants of the particular circuit showra the current-voltage phase relations are those of aninductive circuit. For frequencies lower than 61 cycles the phase relations are those of a capacitive circuit. It was noted that the frequency-for which the rapid rise in current takes place depends primarily upon the saturable inductance and is not critical in resist ance or capacitance. The critical frequency was found to vary approximately linearly with the" number of turns of the inductance. the other hand, the rate of change of current, that is, the

o 4 2,021,754 also be connected across the inductance H but steepness of the curve in the critical region, depends primarily upon the value of the resistance in the circuit. For greater resistance, a less steep characteristic is had, tending in the limit toward a linear circuit. It has been found that this characteristic critical behavior to frequency is a very reliable and reproducible type of phenomena which, since it depends upon the characteristics of the iron, may reasonably be expected to be very constant for a long period of time. No temperature effects were measurably present.

In Fig. 4 I have shown an embodiment of my invention utilizing the frequency sensitive circuit of Fig. l in a frequency control system for rotating machines. A primemover II, which may be a steam turbine or similar 'fluid operated device, as illustrated, or a rotating direct-current or alternating current dynamo-electric machine, is

mechanically connected by means of a shaft I! to operate a pilot generator ll of the alternating current type for producing a voltage which varies proportional to the frequency orthe speed of the prime mover and is connected to energize a control circuit It. The series circuit illustrated in Fig. 1, which comprises the saturable inductance capacitance I2 and resistance II, is connected across the circuit W to be energized in accordance with the voltage of generator I8. Thevoltage across the capacitance i2 is utilized in this case'instead of the resistance I2 to control I an electro-responsive device I! which is utilized to effect control of the speed control mechanism of the prime mover l6.

The electro-responsive device l9 is shown as a contact-making voltmeter comprising a pair of fixed contacts 20 and 2| and a cooperating mov-' able contact 22 which is carried by an arm 22. Thearm 22 is actuated by an electro-magnetic device comprising an armature 24 suitably connected thereto and controlled by a winding 25.

The winding 25 is connected across the capacitance |2 by means of circuit 28'. The contacts 22, 2| and 22 are connected in an electric circuit including a source of current 28 to control a reversible motor 21 by means of its field windings 28 and 29 which are arranged to be energized selectively. The motor 21 is connected to actuate the speed control mechanism of the prime mover, and in the fluid energy type of prime mover as shown I connect the motor 21 to actuate a valve 20 in a fluid supply conduit 20 through a suitable shaft and gearing 2|.

The operation of the arrangement illustrated in Fig. 4 is substantially'as follows: The series non-linear circuit is adjusted by means of the saturable inductance. II to provide a critical region of frequency response within the normal speed of the prime mover ii. For purpose of illustration it will be assu'med'that this region is between 59 and 61 cycles for the pilot generator I! and that 60 cycles corresponds to the normal speed of the prime mover. The steepness of the curve will also be adjusted by means of there- .sistance ll so that the relay is energized tomaintain a stable neutral or non-contact position at 60 cycles. This point of operation will be assumed to be the point N on the curve Ec of Fig. 2. If it be assumed that the frequency increases a slight amount, the energization of the winding 25 .willbe abruptly decreased and the lever 22 of the contact-making voltmeter l9 will move to close contacts 2| and 22 so as to energize the motor 21 through field winding 29. For this connection the motor will be arranged to operate the valve 2! in a direction to decrease the speed of the prime mover. If the frequency decreases a slight amount from the assumed normal'value of 60 cycles the energization of winding 25 will be abruptly increased and the lever 23 will move to close contacts 20 and 22 so as to energize motor 21 through field winding 28. For this connection the motor-will operate in a direction to increase the speed of the prime inover.

In Fig. I have illustrated the arrangement shown in Fig. 4 which employs a rectifying means 32 connected between the capacitance i2 of the non-linear circuit and the operating winding 25 of the contact-making voltmeter. The rectifying means 32 may be of any suitable type, for example, rectifiers of the dry or contact type such as are described in United States Letters Patent No. 1,640,335, granted August '23, 1927, upon an application of Lars O. Grondahl. The rectifying means may be of either the full wave or half wave type. In the circuit arrangement illustrated in Figs. 1 and 4,

power is supplied to the relay mechanism at poor power factor whereas when the rectifier is employed as in the arrangement of Fig. 5, power is furnished at unity power factor with the result that the non-linear circuit may consist of smaller parts. Without the rectifier the varying position of the core sometimes causes objectionable changes inimpedance in the network whereas with the rectifier these changes in impedance are absent because the rectifier insulates the nonlinear circuit from impedance changes in the relay mechanism. When the rectifier is of the dry or contact surface type, the rectifier resistance is an appreciable part'of the total res stance, the decrease in this resistance whch characterizes dry rectiflers serves to limit the voltage applied to the relay winding under abnormal voltage conditions.

a pilot generator of the type In Fig. 6 I haveshown an embodiment of my invention in a speed regulating system for a direct current motor. A direct current motor 33 is provided with brushes 34 through which energy is received from a supply circuit 35. The

motor is provided with a shunt field winding 36 and a control winding 31 which acts differentially therewith as indicated by the arrows. Although may be employed, I have shown an alternative arrangement wherein auxiliary slip rings 38 are provided in such a manner that an alternating voltage varying with frequency may be taken by means of the control circuit I! to energize the frequency responsive non-linearcontrol circuit of the type illustrated in Fig. 1 comprising the saturable reactor II, the capacitance l2 and the resistance II. The field winding 31 is connected to be energized in accordance with the voltage across the capacitance l2 through suitable rectitying means 89 which as shown may be of the dry surface contact type as illustrated in Fig. 5.

The operation of the arrangement illustrated in Fig. 6 is substantially as follows: It will be assumed that the non-linear circuit is adjusted for speed and frequency conditions similarly to the arrangement illustrated in Fig. 4. Under these conditions the winding 81 will be energized by a current proportional to the voltage at the point N in the curve Ec of Fig. 2. Thenet excitation of the motor will be such as to cause the motor to operate at the normal speed. If the speed ina modification of illustrated in Fig. 3

' voltage variations, the

cuit of Fig. 9 may be substituted for the simple 7 has been described in the foregoing arrangements is suitable for use with a source of frequency varying proportional to voltage but there are v other applications where it is desirable to provide a frequencyresponsive means which is independent of variations of the voltage of the source.

In Fig. 7 I have illustrated an elementary circuit diagram of a non-linear network which is sensitive to changes in frequency and relatively insensitive to variations of voltage. This network comprises a branch circuit comprising a series connected saturable reactor 42 and a resistance 43 connected in parallel relation with a branch circuit comprising a capacitance 44 across an alternating source l0 through a load resistance 45. g

If the load current I: through the resistance 45 is measured as a function of the applied voltage,

the curves of Fig. 8 will be obtained wherein the applied voltage is taken as abscissa: and the load current as ordinates for three different frequencies f1, 1: and In. It may be seen that there is a region indicated by the arrows where a change in current with voltage is small or negligible, while a relatively large change in current with frequency exists. trated in Fig. 7 it has been observed that the applied voltage may vary through limits of the order of 110% while the current change may be as small as a fraction of one per cent. However, when the frequency changes by 1%, a change in load current may be as large as 2 or 3%. Thus, when the circuit is supplied froma variable fre-. quency, variable voltage source, the load current Iz,.and hence the voltage across the load resistance 45 varies in frequency and voltage in the manner indicated, the percentage increase in voltage being greater than the percentage involtage source, 4

crease in frequency. This new namely the voltage across the resistance 45 may be used to energize a circuit which is critical to this change of voltage and frequency. This property is had in a series non-linear circuit employing a capacitance, a resistance, and an inductance.

In Fig. 9 I have illustrated diagrammatically the complete circuit comprising the non-linear parallel networkof Fig. 7 having the input circuit indicated by the control circuit III instead 5 In the circuit of'the type illus- 01' the in this figure, in parallel relation with the capacitance l2. voltage across the resistance i3, or the voltage across the capacitance i2, varies critically with the source frequency but substantially independently of variations in the source voltage. will be apparent to those skilled in the art that where regulation or control is desired in response to frequency and substantially independently of frequency sensitive cir- The current I: and hence the quency with observation points marked by a circle,

series circuit of Figs. 4, and 8 in therelation indicated by the circuits II and 25'.

In Fig. I have shown another arrangement suitable for use in the embodiments of my invention illustrated in Figs. 4, 5 and 6, which utilizes a series-parallel type of non-linear circuit for obtaining a frequency responsive means which is independent of voltage variations. The series-parallel branch circuit comprises a saturable reactor H connected in series relation with a parallel branch comprising two arms, one of which includes the saturable reactor 42 in series relation with the resistance 43 and the other of which includes the capacitance 44. The seriesparallel branch circuit is connected in series relation with a resistance across an alternating voltage control circuit lit. The output circuit 25' is connected across the resistance 45 for actuating the control means of Figs. 4, 5 and 6.

For a certain region the current traversing the resistance 45 is constant in wave form and phase of its peak current through substantial variations in applied voltage. shown a characteristic curve plotted between the frequency of the supply as abscissa: and the current in the series circuit as ordinates for two cases (a) voltage varying proportional to freand (b) voltage constant and frequency varying with observation points marked by an 1:. Within the limit of accuracy of measurement the two curves were found to coincide. It may be concluded, therefore, that for this circuit the series current is a function of frequency alone and is independent of voltage in the region under consideration. It may be seen that the current varies more rapidly than the frequency. Thus a 1%,

phenomena depends upon the comparatively,

stable and reproduciblesaturation properties of the saturable inductances,

The frequency-sensitive voltage-independent series parallel circuit of Fig. 10, may be applied to thefrequency control of the generator directly" without the use of a pilot generator by connecting the output circuit 25 in the speed control circuit of Fig.4 as will be evident to those skilled in the art. The current in the output or relay circuit is in this case independent of generator voltage, and hence load, and varies as a function of generator speed and hence frequency alone. In those cases for which sufiicient sensitivity to frequency changes is provided by the circuit illustrated in Fig. 10 the output circuit 25 maybe energized directly inaccordance with the series current. In those cases for which great sensitivity .to frequency is required, the series-parallel type of non-linear circuit may be used in combination with a series-type of non-linear circuit as described below.

In Fig. 12 I have illustrated a modification of the frequency sensitive arrangement shown in Fig. 10 which employs the combination of a seriesparallel non-linear circuit of Fig. '10 and a series type of non-linear circuit comprising a series connected resistance II, a capacitance I2 and a saturable inductance i I connected to be energized In Fig. 11 I have in accordance with the voltage drop across the resistance 4B. The output circuit 25' is connected to be energized in accordance with the current traversing the series non-linear circuit and as shown is connected across the capacitance I2. 5

The series parallel non-linear circuit is connected to be energized from the control circuit l8. Although this particular frequency-responsive circuit involves more component parts it makes available extreme sensitivity to change in fre- 0 quency coupled with independence of voltage. It will be apparent to those skilled in the art that where regulation or control is desired in accordance with extreme sensitivity to change in frequency coupled with independence of voltage, 15 this frequency sensitive circuit may be substituted for the simple series circuit of Figs. 4, 5 and 6 in the relation indicated by the circuits II and 25'.

While I have shown and'described particular embodiments of my invention it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

i. In combination, a rotating machine, means for producing a voltage having a frequency proportional to the speed of said machine, an electric network connected to be energized from said voltage-producing means and including an inductance element varying with current and a capacitance element, said elements being so connected and having volt-ampere characteristics so correlated as to obtain a-condition of nonlinear resonance for producing an electric quantity in said network which changes abruptly at a critical frequency of said voltage-producing means, said critical frequency being at a value higher than the frequency corresponding to maximum current in said network, 'and means connected to be energized in accordance with said electric quantity of said network for controlling the speed of said rotating machine.

2; In combination; a rotating machine, means for producing a voltage having a frequency pro portional to the speed of said machine, an electric network having a non-linear volt-ampere characteristic and including an inductance element varying with current and a capacitance element connected to be energized from said voltage-producing means for producing a current 5.3 in said network varying in accordance with the frequency and'independent of the voltage of said means, a second network including an inductance varying with current and a capacitance connected for non-linear resonance for producing an electric quantity in said second network which changes abruptly at a critical frequency and independently of variations in the voltage of said voltage-producing means, and means connected to be energized'in accordance with said electric quantity of said second network for controlling the speed of said rotating machine.

3. In combination, a rotating machine, speed control means for said machine, an electric generator for producing an alternating voltage vary- '0 ing proportional to frequency and connected to be operated from said machine, an electric network comprising a resistance, a capacitance and mit energized from said generator for producing a current in said network which varies abruptly at a critical value of the frequency of said generator, said critical frequency being at a value higher than the frequency correspondingv to maximum current in said network, and means for energizing said speed control means in accordance with the voltage across said capacitance.

4. In combination, a dynamo-electric machine, means for producing a voltage having a frequency proportional to the speed of said machine, an electric network of impedance elements including a resistance, a capacitance and an inductance varying with current connected to be energized from said voltage producing means, said impedance elements being arranged for non-linear resonance to provide an electric quantity in said network which varies abruptly at a critical value of the frequency of said voltage producing means, said critical frequency being at a value higher than the frequency corresponding to the maximum current of said network, and means connected to be energized in accordance with said electric quantity of said network for controlling said dynamo-electric machine in a manner to maintain its speed substantially constant.

5. In combination, a direct-current dynamoelectric machine, means for producing a voltage having a frequency proportional to the speed of said machine, an electric network comprising a series connected resistance, capacitance and an inductance varying with current connected to be energized from said voltage producing means, said saturable inductance being correlated with said resistance and capacitance so as to produce a current in said network which varies abruptly at a critical value of the frequency of said voltage producing means, said critical frequency being at a value higherthan the frequency corresponding to maximum current in said network, and

'means connected to be energized from said electric network for varying the excitation of said dynamo-electric machine in a manner to maintain its speed substantially constant.

6. In combination, a direct-current dynamoelectric machine having a control winding, means 'for obtaining an alternating voltage from said machine of a frequency varying proportionally to the speed of said machine, a non-linear circuit including an inductance varying with current and a capacitance arranged for non-linear reso- 5 nance and connected to be energized in accord- '.ance with said alternating voltage and having an abrupt change in current above a critical frequency of said alternating voltage, said critical frequency being at' a value higher than the fre- 10 quency corresponding to the maximum current of said non-linear circuit, and means interconnecting said non-linear circuit and said control winding for abruptly changing the energization of said control winding at said critical frequency. 15

7. In combination, a direct-current dynamoelectric machine having a shunt field winding and a field winding acting differentially therewith, means including slip rings for obtaining a voltage from said machine of a frequency varyg0 ing proportionally to.its speed, a frequency responsive non-linear circuit comprising a seriesconnected resistance, capacitance and a saturable inductance having volt-ampere characteristics correlated for non-linear resonance and connected to be energized across said slip rings, and means including rectifying means for energizing said differentially acting field winding in accordance with the voltage across said capacitance.

8. In combination, a dynamo-electric machine having an alternating current output circuit for producing an electric quantity variable in accordance with an operating condition of said machine, means including an excitation winding for said machine for controlling said operating :5 condition, an electric network connected to said output circuit and including an inductance variable with current and a capacitance arranged with said inductance for non-linear resonance to provide an electric quantity in said network which varies abruptly at a critical value of the electric quantity of said output circuit, and means including a rectifier for energizing said winding with direct current variable in accordance with variations in the electric quantity of said network.

CHAUNCEY G. SUITS. 

